Genitourinary Cancer

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SU_30_2302 - Predictive Factors for Urinary Toxicity from a Multi-Center Trial of Stereotactic Body Radiation Therapy for Prostate Cancer

Sunday, October 21
1:15 PM - 2:45 PM
Location: Innovation Hub, Exhibit Hall 3

Predictive Factors for Urinary Toxicity from a Multi-Center Trial of Stereotactic Body Radiation Therapy for Prostate Cancer
R. Meier1, A. C. Beckman2, G. Henning3, S. A. Woodhouse Jr4, S. K. Williamson5, N. Mohideen6, J. J. Dombrowski7, R. L. Hong8, P. W. Linson9, and I. D. Kaplan10; 1Swedish Cancer Institute, Seattle, WA, 2Central Baptist Hospital, Lexington, KY, 3Huron River Radiation Oncology, Brighton, MI, 4Community Cancer Center, Normal, IL, 5Capital Health Medical Center, Pennington, NJ, 6Northwest Community Hospital, Arlington Heights, IL, 7Saint Louis University, St. Louis, MO, 8George Washington University School of Medicine, Washington, DC, 9Scripps Clinic Radiation Therapy Center, Vista, CA, 10Beth Israel Deaconess Medical Center, Boston, MA

Purpose/Objective(s): Stereotactic body radiotherapy (SBRT) is an emerging therapy for early-stage prostate cancer. Published data describing appropriate patient-selection parameters and dose-volume constraints are limited. We sought to determine patient and treatment parameters associated with increased rates of genitourinary (GU) toxicity.

Materials/Methods: Twenty-one hospitals enrolled 309 patients with biopsy-proven adenocarcinoma of the prostate: 172 low-risk (CS T1-T2a, Gleason 6, PSA < 10 ng/mL) and 137 intermediate-risk (CS T1c-T2b with either Gleason 7 and PSA < 10 ng/mL, or Gleason 6 and PSA between 10 and 20 ng/mL). All patients were treated with a non-isocentric robotic SBRT platform using real-time tracking of implanted fiducials. The prostate was prescribed 40 Gy in 5 fractions of 8 Gy. Heterogeneity and normal tissues were constrained (Dmax 48.3Gy or urethra V47Gy <20%; rectal V36 Gy <1 cc; bladder V37 Gy <5-10 cc). No patient had concomitant or adjuvant androgen ablation therapy. Patient characteristics (race, age, performance status, risk group, previous transurethral resection of prostate, baseline AUA score) and dose-volume/treatment parameters for the target and urinary tissues were prospectively recorded. Toxicities were assessed using CTCAE v3; patients with grade 2+ genitourinary (GU) toxicities were compared against those with grade 0-1 GU toxicities. Comparisons were also made for patients with late (>3 months after treatment) grade 2+ GU toxicities. Comparisons between toxicity and non-toxicity cohorts were assessed using the chi-square test for categorical variables, and 2-sample t-test for continuous variables. Cox proportional regression analysis was used in multi-variate analyses. Alpha <0.05 was considered statistically significant.

Results: On univariate analysis, increased grade 2+ GU toxicity was associated with greater baseline AUA score, prostate volume, and bladder D5cc. On multivariate analysis, only AUA score and prostate volume correlated with increased GU toxicity (p=0.045 and p=0.027, respectively). Intraprostatic Dmax and overall treatment duration did not correlate with greater toxicity. The only parameter associated with increased late GU toxicity was pre-treatment TURP (p=0.02): grade 2+ toxicity occurred in 35% of patients with prior TURP versus 12% in those without.

Conclusion: In this trial of five-fraction prostate SBRT delivered with rigid dose constraints and restricted heterogeneity, only baseline AUA score and prostate volume were associated with increased grade 2+ GU toxicity. Pre-treatment TURP was associated with greater rates of late Gr2+ toxicity. This should be considered in selecting therapy for early stage prostate cancer.

Author Disclosure: R. Meier: Research Grant; Accuray. A.C. Beckman: None. G. Henning: None. S.A. Woodhouse: None. S. Williamson: None. N. Mohideen: Independent Contractor; Northwest Community Hospital, Arlington Heights,IL. Partnership; Northwest Community Hospital Physician Cooperative. Chair, Radiation Oncology Committee; ACR Economics and Health Policy. Board Member; The Radiosurgery Society. J.J. Dombrowski: None. P.W. Linson: None.

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